Feature: Thermal management


noble metals are oſten used for conductors, to ensure low resistive loss, corrosion resistance and consistent performance over decades. Te dielectric layers are also applied with precise thickness control to achieve exact impedance targets and reduce parasitics, which is critical for multi-gigahertz wireless operation. Space-qualified thin-film substrates are


manufactured to far tighter tolerances and can be subjected to extensive screening and testing before integration. Tis includes thermal cycling, random vibration and shock testing to ensure performance. Across all these military and aerospace


applications, thin-film patterned substrates are designed and screened to the highest- level reliability standards, such as MIL- PRF-38534 for hybrid microcircuits and MIL-STD-883 for environmental and mechanical stress testing. Such a combination of precision, thermal performance and rugged construction makes them one of the few substrate technologies capable of meeting the performance and reliability expectations of modern defence and space electronics.


Substrate selection Tus, selection of the correct substrate is key, because of the influences on the mechanical and electrical function of a design. Johanson Technology offers several


dielectric values and different metallisation schemes to meet the needs of its customers. Te substrates can be metallised or non- metallised; see Figure 1. Metallised substrates


can be patterned to customer specifications by chemical or abrasive etching and patterned plating. Single-sided or double-sided metallisation


is available too, and each side can have unique design requirements and metallisation for specific uses. Adhesion layers like titanium-tungsten


or chromium help the metal stick firmly to the ceramic, while gold, copper or nickel, for good conductivity, solderability and compatibility with wire bonding. Te thickness of the gold layer is controlled so that the wire bonds stay strong over time. In applications where heat conduction


is critical, such as in the vacuum of space, engineers must consider thermal conductivity of available substrates or use filled vias as an alternative thermal path within the design. Attention should also be given to the


coefficient of thermal expansion (CTE) and thermal conductivity parameters of the circuits. Spaceborne applications can see large temperature swings from external sources (like solar radiation), while higher power systems can create higher operating temperatures during operation. Tese higher temperatures must be mitigated during the design process. Aluminium nitride, specifically,


conducts heat extremely well, spreading it away from hot components, extending their lifetime, while alumina (aluminum oxide, Al2O3) offers strong mechanical stability and high voltage tolerance. Special “filled vias” inside the substrate


Figure 1: Johanson offers a wide range of dielectrics materials in lapped, polished or “as fired” condition. These substrates can be metallised, with patterns, or non-metallised


lower thermal resistance and electrical inductance, helping both with heat transfer and maintaining clean signal paths. Johanson Technology incorporates vias


into substrate designs with demanding requirements; see Figure 2. Vias can be offered as either filled, through-hole or plated-through. Te process involves lasering through a substrate from the top to bottom layer and then sputtering or plating over the substrate via opening. Both options are effective in routing electrical signals from one side to another.


Figure 2: Johanson has advanced experience incorporating vias into substrate with demanding requirements. Vias can be offered as either filled, through-hole or plated-through


Figure 3: In military and aerospace systems, thin film patterned substrates are often the foundation for the most critical electronic assemblies


www.electronicsworld.co.uk September 2026 31


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